The present invention relates to thermal protection devices and more particularly a thermal protector suitable for guarding semiconductor devices from slow and prolonged temperature increases.
As is known, very frequently semiconductor devices are equipped with protection devices only against power supply transients characterized by strong voltage values, even if of very short duration, for the immediate purpose of preventing damage that can be caused by exposure even to very short voltages higher than those which the semiconductor devices can withstand. For this purpose one uses devices, mostly electronic, particularly adapted to attenuate these voltage peaks and characterized by extremely rapid action times, for example of the MOV (Metal Oxide Varistor) type, Zener diode and others.
In some circuit applications, however, it has been found that the semiconductor device may be subject to voltage and/or current increases of low values but of very long duration (even several minutes). This type of disturbance may cause a slow rise of the temperature of the semiconductor device above the permitted limits, causing breakage or at least malfunction due to thermal drift. It is clear, therefore that for that kind of disturbance the rapid-action electronic protective devices for voltage or current peaks do not represent an effective solution, as their intervention, if it occurs, does not occur in time to prevent the damage or malfunction.